1. Field of the Invention
This invention relates to a reactor for use in a system for decomposing organic oil or fat containing PCB (polychlorobiphenyl) and thereby making it nonpoisonous. More particularly, it relates to a PCB decomposition reactor for mixing PCB with water, an oxidizing agent and sodium hydroxide and effecting its thermal decomposition at high temperature and under elevated pressure.
2. Description of Related Art
FIG. 3 illustrates an example of a conventional reactor for use in PCB decomposition system. In this reactor, a feed pipe 23 for feeding a mixture 22 of water, PCB, mineral oil and sodium carbonate to a hollow reaction vessel 21 is connected to the lower part of its side wall. Moreover, reaction vessel 21 is equipped with pipes 24 and 25 which connect the upper part of its sidewall and feed pipe 23 in flow communication relationship, and a circulating pump 26 for agitating purposes is installed between pipes 24 and 25.
An outlet pipe 28 for supplying the reaction fluid to a cyclone separator 27 is provided at the top of reaction vessel 21. The top of cyclone separator 27 is equipped with a discharge pipe 29, which is connected to the equipment constituting the downstream side of the PCB decomposition system. The bottom of cyclone separator 27 is equipped with a recirculation pipe 30, the other end of which is connected to reaction vessel 21. Moreover, a gas supply nozzle 32 for supplying air or oxygen 31 is connected to the bottom of reaction vessel 21.
When the PCB decomposition reactor having the above-described construction is operated, reaction vessel 21 is supplied with water at 250 kgf/cm.sup.2 and 380.degree. C., and also with PCB, mineral oil and sodium carbonate. Circulating pump 26 serves to agitate the reaction fluid within reaction vessel 21, and also introduce the reactant mixture 22 of water, PCB, mineral oil and sodium carbonate having a temperature of 200 to 250.degree. C. from the outside into reaction vessel 21 by mixing it with the steam of the fluid driven by circulating pump 26. This mixture 22 undergoes an exothermic reaction within reaction vessel 21 and causes sodium carbonate to precipitate.
At the bottom of reaction vessel 21, air or oxygen 31 is injected from gas supply nozzle 32. This air or oxygen 31 serving as an oxidizing agent dissolves in the reaction fluid while it goes up through reaction vessel 21 in the form of gas bubbles, thus causing an agitation flow within reaction vessel 21. The sodium carbonate precipitated within reaction vessel 21 is agitated into contact with PCB by the circulation flow caused by circulating pump 26 and the stream of gas bubbles injected from gas supply nozzle 32, so that the decomposition reaction of PCB is accelerated.
As described above, the conventional reaction vessel 21 has used sodium carbonate in order to decompose PCB. The solubility of sodium carbonate decreases with rising temperature, and it scarcely dissolves at temperatures above 350.degree. C. Consequently, it has been conventional practice to feed the mixture 22 of water, PCB, mineral oil and sodium carbonate having a temperature of 250.degree. C. to reaction vessel 21 having a temperature of 380.degree. C. and thereby precipitate the sodium carbonate within reaction vessel 21 in the form of solid particles. The precipitated sodium carbonate, together with the introduced fluid, is agitated by gas bubbles of oxygen. Thus, a so-called three-phase fluidized bed consisting of a solid, a gas and a liquid is formed to accelerate the decomposition reaction of PCB.